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Operating Systems BSD FreeBSD abnormal permission changes in /home Post 302521322 by brightstorm on Tuesday 10th of May 2011 11:45:15 PM
Old 05-11-2011
FreeBSD abnormal permission changes in /home

Hi,

I have a bit of a headache with a server doing some rather mysterious yet static changes to permissions in /home. The server in question is a FreeBSD server. It's an older beast with quite a few custom tweaks and now I'm stuck with it :-)

The problem is that some of the directories in /home will get their owner and group changed to a numeric value. The value does not have anything in common with UID or GID and when a temporary fix is made (chown user:user user), it's a matter of time before it happens again. It may happen within 24 hours or within a week, there seems to be no indicator.

The numeric value for each user will remain the same. This sounds a bit weird, but consider this:

Before the change:
Code:
brightstorm:brightstorm brightstorm (owner, group, (home)dir)
otheruser:otheruser otheruser

After the change:
Code:
192382:192382 brightstorm (again - owner, group, (home)dir)
934329:934329 otheruser (owner/group values are made up for this example)

Then we chmod it back.
Code:
brightstorm:brightstorm brightstorm (owner, group, (home)dir)
otheruser:otheruser otheruser

Next time it happens, same values.
Code:
192382:192382 brightstorm
934329:934329 otheruser

Since we have a large serverfarm my first instinct was to check for suspicious crontab entries - none found.
I then checked root's authorized keys to see if any old timers would have some kind of (horrible) remote "cleanup" - none found.
I have been knee-deep in pretty much /var/log* - especially auth.log, cron, messages, etc. for good measure, but there is really no indicator.

I know little about the machine itself besides that it's a virtual guest on a VMWare host. I wrote a workaround script to look at /home every 5 minutes and pull anything with an odd looking (numeric) owner and fix permissions by taking the name of the homedir and chown the poor people's functionality back, because this problem effectively prevents them from writing anything in their homedir.

I know I may be leading you on a wild goosechase here because of the tricky element that the server is a modified FreeBSD and is an older version back from 2003. (One can reason that it need upgrading but a lot of legacy are preventing us for doing so at the moment), but I am very curious if any of you have seen similar behaviour before or would have any other suggestions on where to look for culprits.

/Klaus
 

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CHOWN(8)						    BSD System Manager's Manual 						  CHOWN(8)

NAME
chown -- change file owner and group SYNOPSIS
chown [-fhv] [-R [-H | -L | -P]] owner[:group] file ... chown [-fhv] [-R [-H | -L | -P]] :group file ... DESCRIPTION
The chown utility changes the user ID and/or the group ID of the specified files. Symbolic links named by arguments are silently left unchanged unless -h is used. The options are as follows: -f Don't report any failure to change file owner or group, nor modify the exit status to reflect such failures. -H If the -R option is specified, symbolic links on the command line are followed. (Symbolic links encountered in the tree traversal are not followed.) -h If the file is a symbolic link, change the user ID and/or the group ID of the link itself. -L If the -R option is specified, all symbolic links are followed. -P If the -R option is specified, no symbolic links are followed. Instead, the user and/or group ID of the link itself are modified. This is the default. Use -h to change the user ID and/or the group of symbolic links. -R Change the user ID and/or the group ID for the file hierarchies rooted in the files instead of just the files themselves. -v Cause chown to be verbose, showing files as the owner is modified. The -H, -L and -P options are ignored unless the -R option is specified. In addition, these options override each other and the command's actions are determined by the last one specified. The owner and group operands are both optional; however, at least one must be specified. If the group operand is specified, it must be pre- ceded by a colon (``:'') character. The owner may be either a numeric user ID or a user name. If a user name is also a numeric user ID, the operand is used as a user name. The group may be either a numeric group ID or a group name. If a group name is also a numeric group ID, the operand is used as a group name. For obvious security reasons, the ownership of a file may only be altered by a super-user. Similarly, only a member of a group can change a file's group ID to that group. DIAGNOSTICS
The chown utility exits 0 on success, and >0 if an error occurs. COMPATIBILITY
Previous versions of the chown utility used the dot (``.'') character to distinguish the group name. This has been changed to be a colon (``:'') character, so that user and group names may contain the dot character. On previous versions of this system, symbolic links did not have owners. The -v option is non-standard and its use in scripts is not recommended. LEGACY DESCRIPTION
In legacy mode, the -R and -RP options do not change the user ID or the group ID of symbolic links. SEE ALSO
chgrp(1), find(1), chown(2), fts(3), compat(5), symlink(7) STANDARDS
The chown utility is expected to be IEEE Std 1003.2 (``POSIX.2'') compliant. HISTORY
A chown utility appeared in Version 1 AT&T UNIX. BSD
March 31, 1994 BSD
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